A video compression method as defined in the opening paragraph has been standardized by the Motion Frames Expert Group and is well-known as MPEG1 or MPEG2. The known method includes transformation of video pixels into frequency coefficients, quantization of said coefficients, and variable-length coding of the quantized coefficients. The quantization is controlled so as to achieve a desired quality or bit rate of the compressed signal.
The MPEG compression method produces I, P and B-frames. I-frames are encoded autonomously, i.e. without reference to another frame. P-frames are predictively encoded with reference to a previous (possibly motion-compensated) I or P-frame. B-frames are bidirectionally predictively encoded with reference to a previous and a subsequent I or P frame. B-frames are not themselves used as reference for encoding other frames.
The concept of B-frames in MPEG provides maximum encoding efficiency. However, the use of B-frames roughly doubles the complexity, memory capacity and memory bandwidth. In view thereof, MPEG encoders have been developed which produce I and P-frames only (“IP encoders”). A disadvantage of IP encoders is their efficiency. They need approximately 10–20% more bit rate than IPB encoders.